The present invention relates to a carburetor of a gasoline engine and, more particularly, to improvements in an electronically controlled carburetor.
In general, a conventional carburetor needs some adjustment for the unevenness of the carburetor characteristic depending on the accuracy of manufacturing of the low-speed fuel supply system or the main fuel supply system and the improper stoichiometric mixture ratio caused by aging due to the abrasion of a throttle valve shaft or accumulated dust in bleeds or metering orifices. One of the approaches to this adjustment uses an oxygen sensor attached to an exhaust pipe to sense the components of exhaust gas and to effect a feedback control for the adjustment. The approach, however, involves the following problems. It is difficult to effect feedback control in the operating region where the temperature of the exhaust gas is low, and also to apply feedback control to a mixture ratio other than the stoichiometric mixture ratio. In addition, the control response is relatively slow.
The conventional carburetor control takes advantage of the negative pressure that exists in the venturi. For this reason, when a car is driven at a high elevation where air density is low, the air-fuel ratio of the mixture will change.